1. Field of the Invention
The present invention relates to the recovery of gallium values from basic solutions containing such values, for example the sodium aluminate solutions emanating from the Bayer process for the production of alumina.
This invention especially relates to the extraction of gallium values from solutions comprised thereof by means of a substituted hydroxyquinoline extractant.
2. Description of the Prior Art
The recovery of the gallium values present in alkaline aqueous solutions via liquid/liquid extraction by contacting such solutions with an organic phase containing an extracting agent (extractant) and an organic solvent, and back-extracting the gallium values by washing the organic phase into which said gallium values have been transferred with an aqueous acid solution, is known to this art; compare French Patents Nos. 2,277,897, 2,307,047, 2,307,882, 2,495,601, 2,532,295 and 2,532,296.
It is also known to this art to employ a resin as a support for the extracting agent and to extract the gallium values by flowing the alkaline solution over this resin. Analogously, the gallium values are recovered by washing the resin charged with gallium with an acid solution. Thus, published Japanese Patent Applications No. 60/042,234 and No. 58/96,831 and published European Patent Applications Nos. 258,146 and 265,356 present examples of suitable resins which can be used as supports for the extractant, which extractant is identical to that used in the above liquid/liquid extraction process.
These processes of liquid/liquid extraction or flow over a resin containing the extracting agent entail, in brief, transferring the gallium values contained in the basic solution into the medium (organic phase or resin) containing the extractant by intimately contacting these two media with each other. In a second step, the gallium values are back-extracted by contacting the medium (organic phase or resin) charged with the gallium values with an aqueous acid solution. The acid solution thus recovered can then be purified by numerous processes to remove the cations co-extracted with the gallium, such as, for example, sodium and aluminum. The purification processes described in French Patents Nos. 2,495,599, 2,495,600 and 2,495,601, assigned to the assignee hereof, are exemplary.
The purified solution then serves as a starting material for the production of gallium metal or of compounds containing gallium.
Gallium is generally present in the form of impurities in natural minerals and, more particularly, in the aluminum minerals such as the bauxites.
Consequently, the major proportion of the gallium produced is recovered from the sodium aluminate solution or Bayer liquor circulating in the Bayer process for the recovery of alumina.
After recovery of the gallium, such Bayer liquor is recycled back into the Bayer process cycle.
As this Bayer liquor is very highly basic, a significant amount of sodium ions will be extracted when it is contacted with the extracting medium, rendering the latter likewise highly basic. It is therefore necessary, in the processes currently characterizing the state of this art, to neutralize such basicity during the back-extraction of the gallium by means of an acid solution, thus necessitating consumption of a great amount of acid.
Moreover, it will also be necessary to adjust the pH of the Bayer liquor recycled back into the alumina production cycle, by the addition of sodium hydroxide thereto, in order not to disrupt proper operation of this cycle.